If you see an error like the following when trying to open Outlook, it may be caused by Lync accessing your .ost file:
To resolve this problem and allow Outlook to open:
- Exit Lync. To do this, click the triangle next to the gear icon, then choose File > Exit:
- Wait a moment for all of Lync's processes to quit, and then try opening Outlook again.
- Once Outlook is running, you can run Lync again.